As demand for further higher integration of semiconductor devices increases (LSI), additional patterns not directly related to the electronic circuit of a device, such as a moisture resistant ring pattern, that have comparatively loose design rules to those of the integrated circuits must also be miniaturized.
FIG. 1 is a plan view showing an example of a conventional photomask 10 utilized for patterning semiconductor devices. The peripheral and unpatterned areas in the figure depict an opaque region of the photomask which is conventionally formed of a shading film made from metal such as Cr. The patterned parts depicted in the figure is a transparent region that transmits a light for patterning. Moreover, the broken line 11 in the figure is a virtual line equivalent to a scribe line. A semiconductor substrate is cut along the scribe line, and divided into individual chips in the final process of manufacturing a semiconductor device. Therefore, the area inside the broken line 11 means one chip. In FIG. 1, the area inside the broken line 11, equivalent to a scribe line, is the area of a single chip and the area outside of the broken line is a shaded area that is conventionally not patterned.
The photomask 10 of FIG. 1 has a circuit pattern 12 to form an electronic circuit and a moisture resistant ring pattern 13 to form a moisture resistant ring. Moreover, FIG. 1 depicts the circuit pattern 12 schematically by the symbol “F”, though an actual photomask has a pattern for forming a wiring or a contact hole as the circuit pattern on the chip.
As further shown in FIG. 1, the wiring, the contact hole, the moisture resistant ring (moisture proof ring), and other patterning are formed by setting the photomask 10 in an exposure device, and printing (transcribing) the circuit pattern 12 and the moisture resistant ring 13 onto the semiconductor substrate. The moisture resistant ring is provided to prevent the incursion of moisture into a completed semiconductor device that is liable to cause a breakdown. Usually, the moisture resistant ring is formed two or threefold as shown in FIG. 1. Moreover, the moisture resistant ring pattern 13 is usually formed with a near identical width as the circuit pattern. This is because, if the width of the moisture resistant ring is significantly larger than the width of the circuit pattern, it generates a phenomenon called loading effect in which the etching speed in the moisture resistant formation part becomes slower than the etching speed in the circuit formation part. As a result, the moisture resistant ring cannot be formed properly. The moisture resistant ring pattern 13 usually has a width of about 0.4 μm in the photomasks used for manufacturing a semiconductor device employing 90-nm design rules.
During the manufacturing process, or when otherwise in use the photomask 10 might be charged with static electricity. When the photomask 10 is carrying a static electric charge, and the inside and the outside of the conventional photomask are electrically separated by the moisture resistant ring pattern 13 as shown in FIG. 1, potential difference might be generated between the inside and the outside of the moisture resistant ring pattern 13. As a result, the moisture resistant ring pattern 13 might be damaged by a static electric discharge.
Therefore, a photomask that can prevent patterns from being damaged by static electricity and a manufacturing method of a semiconductor device by using the photomask are required.